Signal transmission system



Odi. 17, 1933. Q N NEBEL SIGNAL TRANSMISSION SYSTEM Filed March 27. 1931 wlm. C

/V VEN TOP C. N. NEBEL By. 9U! j A TTOPNEV m2 ummm mnw Il... CME ,Pw mmm mg L mall Abw TIL: Jf nw Q Y o NN Patented Oct. 17, 1933 f L UNITED STATES l. t Y 1,931,031

SIGNAL TRANSMISSION SYSTEM i Charles N. Nebel, Newark, N. J., assigner to Bell Telephone Laboratories,

Incorporated, New e York, N. Y., a corporation of New York Application March 27, 1931. Serial No. 525,643

claims. (c1. lis-44) This invention relates to signal `transmission systems and particularly to telephone cable systems which are electrically long.

An object of this invention is to minimize 5 delays andv hangover effects in electrically long telephone systems having large delays in transmission.

A further object of this invention is to make a cable system operate in a more eflicacious manner `and with less apparatus than heretofore used. Y

Electrically long transmission systems of great attenuation between repeaters are generally arranged to transmit signals in one direction at a time. nearby terminal repeater actuate the control means to condition the repeater to transmit the voice currents to the line. Of thetwo persons conversing over the line the first to begin to talk controls the repeater lat his terminal by circuits which introduce a portion of the. voice energy into the controlling apparatusiforconnecting the repeater in the proper direction for transmission. In a certain type of system aso-called courier current is sent out in advance of the voice currents to condition the repeater at the distant terminal for reception of those Voice currents. United States patents to H. AA. Barton 1,574,781 issued March 2, 1926,13.` C. Mathes 1,678,188 issued July 24, 1928 and H. D. Arnold 1,565,- 302 issued- December 15, 1925 disclose several such arrangements.- Thesev circuits employ either the same or the same type of electrical transmission lpath for both the apparatus controlling current and for the speech current. Delay circuits are usually employedv todelay the voice currents for an interval of time so that theV courier current may proceed ahead of the voice currents to condition the distant repeater for transmitting the message waves in the proper direction.

Controlling currents have alsobeen used `in systems wherein the message waves are delayed for a denite interval of time sufficient to insure that the controlling current has already conditioned the distant terminal station for proper transmission of the message waves before therlatter are released by the nearby terminal station. This method obviates the possibility of the terminal apparatus at both ends of a transmission line being conditioned at the same time. Such an event otherwise could occur when a controlling current has been sent out from the distant terminal station very shortly before the transmission oi' the controlling current from the Subscribers voice currents entering the` the message waves.

nearby terminal station,l `but not suiciently ahead intime to have prevented the transmission of the controlling current from the near-` by station. The circuit for preventing such occurrence is termed an anti-lockout "arrangement. The use of the courier inan` iantilockout system materially increases-the time required for a party ceasing to talk to hear the first word in reply over the time required when such a system is not used. Y y .A i

In a system in accordance with fthe principles underlying this invention the controlling or courier current is transmitted? over a` separate circuitor a separate channelhaving a higher speed of transmission than that used for the message waves. lThis high velocity circuit for the courier currentemay'be an `openwire circuit, non-loaded circuit, loaded openwire circuit, Vphantom circuit, radio circuit, `car- '15 rier circuit or any type of circuit having a shorter time of transmission than that used for If the voice currents are transmitted over a loaded cable, `rthen a nonloaded cable circuit having the sameV gauge conductor or a larger gauge conductor than -the loaded circuit may be used for the controlling or courier current. e i

The time of transmission of any of thev above mentioned rcontrol circuits should be shorter than for the loaded cable circuit forfthe message waves, the radio circuit having the shortest time of transmission. n

This new method of control appreciably decreases the amount' of artiiicial delay neces- 90 sary at the terminal station nearest the talker and makes the overall transmission time less and, in some cases, eliminates the useof Yartificial delay circuits altogether. f

An advantage of this method of control is L that one, circuit may be used for the transmis- Sion `of Va large-number of` couriers to control different paths of speech transmission.- .If con- .to land lines 11 and12.

London cable system would be about 1400 miles long. For a No.` 19 gauge telephone cable, heav ily loadedwith an inductance of 44 millihenrys per loading section of 6060 feet, between New York and Newfoundlandthe time of transmission, including articial delay, would be about .092 second. 'By using this invention the usual delay circuits at New York may be omitted from the voice circuit and the overall transmission time made less by .022 second which is the time of delay in the artificial circuit.

A feature of this inventionl is that the New York technical operator can change operating adjustments of the equipment at'Newfoundland by changing the amplitude of the controlling or courier current. effected by providing a device in the high velocity channel at Newfoundland which is sensitive to av change in amplitude variation Vin the .courier or controlling current. ,This device may be arranged to change the gain Iin anl amplifier circuit if desired. K

Asystem arranged in accordance with this inventionwill now be described with reference "to the ldrawing in which:

Fig. 1 represents one half of this system show- "ing in detail the arrangement of apparatus` "thereat; and Y Y YVTC` is illustrated as having` a terminal station B and a repeater station A. v

The repeater station A comprises essentially lrampliers AEk and AW connected to a subscrib- `ers line section TL'through hybrid coil l0 and The line section is shown balanced by network N. Bridged across the repeater path east in front of AEvis amplier detector unit AD. A similar' unit AD is bridged across the path transmitting Westy in 'front ofA amplifier AW. These units areof a type well known inthe art, the detailed arrangements being illustrated, for example, in

United States Patent 1,560,543 to G. Crisson,

November 10, 1925 and include suitable vacuum` tube amplifying and` rectifying apparatus for vrectifying the voicecurrents to operate relays.

At terminal stationB are amplierslA'E and A'W and amplifier detector unit AD which .are Vsimilar to amplifiers AE and AW and amplier detector units AD and AD' respectively, `which arelocated at station A.:

When voice rcurrents kare transmitted from west to east the unit AD 'will vactuate relay -C Yto cause its normally closed contact toopen.

.This contact normally short-circuits a source of oscillations G. v When AD is actuated in re-v sponse to voice currents transmitted from west Ato-east the contact at relay C is opened and the generator (frA at. once transmits oscillations of `the frequency of the generator over high Vve-Y locity vchannel 13.to terminal station B, where,

vafter ypassing through band-pass iilter l14 the ing, opens the receiving orfeast to west path so that 'the voice currents. transmitted from kB cannot und' their way back to the subscriber.

Channels 11 and 12 are used for the transmission Vof the voice currents and Aare" slower Such adjustments Vmay be velocity channels than courier controlling channel 13.

Fig. 2 shows the system as a whole. It is to be understood that the terminal apparatus and associated equipment at the other end of TC is identical with that illustrated at the near end of cable TC. Consequently, the operation vof the system Yas itf affects only one set of 'repeater and terminal stations will be described.

When voice currents are transmitted from west to east they pass through hybrid coil 10 Vand are amplified by AE prior to passing over channel 11. Before reaching AE a portion of the voice currents enter amplifier detector unit AD which actuates relay C. Relay C' in operating, opens the short circuit around high velocity channel 13 and permits oscillations from genera-V tor Gf to be sent out to station B. High velocity channel 1S may comprise any type of channel having better propagation characteristics than those Vof the voice channels, so that the courier frcrnvG will-arrive at B and condition the terminal apparatus for transmitting over cableV TC before the voice 'currents arrive. This channel may be an open-wire circuit, non-loaded vcable circuit, loaded land circuit, phantom circuit, or

any type cf circuit having a shorter time of transmission than that used for the transmission ci message waves.

tuate amplifier detector AD, in turn, operating relays Dv and Relay D,'as hereinbefore described, will close through the voice channel 1l tocable TC. Relay E will open the east to west path'at its contacts to prevent the voice currents transmitted by B from reentering the system over voice channel 12. 'Y When the west Vstation is in its normal condi.-

V The courier oscillationstransmitted by G pass through iilter 14 and ack tion, currentv from the east station Vwill Vfollow the east to west ypath and will pass through vthe contacts oi relay E and be ampliedby amplifiers AWl and AW. `A portion of thevoice currents arriving at the west-repeater station will Venter ampliierv detector ADand cause the operationA of relay F which will fopen the courier transmitting ThisY will prevent'the-transmission of courier currents from generator G in the event that-thesubscriber at the'west station desires lto speak at thistime.vr Y

it is to be understood, of course, that a single iiiglfr velocity line comprising'several channels may 'be used to condition several different circuitsan'd that'iilter circuits maybe used to sep@- arate 'courier currentsof kdifferent frequencies. The ampliiier detector units at; the terminal Vstations -may be designed, in a manner well known in the art, Ito be highly selectiveof any desired frequency. If l considered desirable,

chazni'el 13 may also `be used for other purposes such, as changing'operating adjustments at the distant terminal station. This may be effected by changing the amplitude of the courier trans. mitted over 13 and inserting an amplier detector at thedistantterrninal which is sensitive to changes in amplitude for accomplishingany dechannel over the message wavechannels to condition the fdistant apparatus before the voice currents arriveat that distant station. Delay circuits having a very slight delay may bev employed, if considered desirable, lparticularlyV in cases whereinthe gain in transmission time of the high velocity channel over the voice channels may not be sufficient, in itself,to permit the distant station to bek conditioned for a predetermined interval of time before the voice currents arrive 'at that station. In suchcases, the artificial delay inthe circuit 'is appreciably less than the delay necessary whena highvelocity channel is not employed. v

It Vis to be understood,of course, that thisinvention may bev used, with slight modifications, in various other organizations Without departing from the scope thereof, and that it is not limited to a courier current for conditioning the distant station but may employ a portion of the Voice currents for that purpose.

What is claimed is:

1. A two-way communication system comprising in combination a first terminal station and a second terminal vstation between which alternate transmission in opposite directions isv to be had, a submarine cable connecting the terminal stations for transmission of signal current, a repeater station connected to the first terminal station by a rst land line for trans` mission of signal current, said first land line havingexclusive of any delay network anywhere in the communication system-a denite transmission time, apparatus effective upon and controlled by the beginning of transmission of signal current from the repeater station to the first terminal station to send courier current to condition apparatus at the first terminal station for transmission of the signal current over the submarine cable to the second terminal station, and instrumentalities for causing the courier current to arrive at the first terminal station before the arrival of the signal current transmitted from the repeater station, said instrumentalities including a second land line connecting the repeater station to the terminal station, said second land line having-exclusive of any delay network anywhere inthe system-a transmission time shorter than said definite transmission time, and instrumentalities for causing the courier current to traverse the second land line.

2. A two-way communication system comprising in combination a first terminal station and a secondrterminal station between which alternate transmission'in opposite directions is to be had, a transmission channel connecting the terminal stations for transmission of signal current, a repeater station connected to the first terminal station by a signal current channel for transmission of signal current, said signalA current channel havingexclusive of any delay network anywhere in the communication system-a certain propagation characteristic, apparatus effective upon and controlled by the beginning of transmission of signal current from the repeater station to the vfirst terminal station to send courier current to condition apparatus at the first terminal station for transv mission of the signal current over the transmission channel to the second terminal station, and instrumentalities for causing the courier current to arrive at the first terminal station before the arrival of the signal current transmitted from the repeater station, said instrumentalities including a courier current channel connecting the repeater stationto the terminal station, said courier current channel havingexclusive fof any delay network anywhere in the 4communication system-a propagation characi minal stations for transmission of signal cur` rent, a' repeater station connected to the first terminal station by a signal current channel, apparatus effective upon and controlled by the beginning of transmission of signal current from the repeater station tov the first terminal station to send courier current to` condition apparatus at the `first terminal station vfor transmission of signal current over the transmission channel to the second terminal station, and instrumentalities for causing the courier current to arrive at theV first terminal station `before the arrival of the signal current transmitted from the repeater station, said instrumentalities including a courier current channel connecting the repeater station to the terminal station, and transmission apparatus for causing the courier current to traverse the courier current channel, said courier current channel comprising a medium which. hasexclusive of any delay network anywhere in the communication system-a `higher transmitting Velocity than the signal current channel.

4. A two-way communication system comprising inA combination a first terminal station and a second terminal station between which alternate transmission in opposite Vdirections is to be had, atransmission channel connecting the terminal stations for transmission of signal current, a repeater station connected to the first terminal station by a signal current channel, normally operable circuit conditioning apparatus `effective upon and controlledby the beginning ofrtransmission of signal current from the repeater station to the first terminal station to send courier current to condition apparatus at the firstv terminal station for transmission of signal current over the transmission channel to the secord terminal station, and instrumentalities for causing the courier current to arrive at the first terminal station beforevthe arrival of the signal current transmitted from the repeater station, said instrumentalities including a cou- Arier current channel connecting the repeater station to the terminal station, transmission apparatus for causing the courier current to traverse the courier current channel, said courier current channel comprising a medium which has-exclusive of any delay network anywhere in the communication systemaA higher transmitting velocity than the signal current channel, and receiving apparatus responsive to the reception by the first terminal station of signal current transmitted by the .second terminal station over the transmission channel `for disabling said normally operable circuit conditioning apparatus. Y

5. A two-way communication system compris'- ing in combination a first terminalstation and had, a transmission channel connecting the terminal stations for transmission of signal current, a repeater station V,connected to the first terminal station by a signal current channel having-exclusive of any ldelay network anywhere in the communication system-a denite rtransmission time, normally kdisabled apparatus at therst terminal station for .transmission of signal current over .the transmission'channel to the second terminal station, normally operable apparatus at the rstterminal station for the vreception of signal current transmitted by the VsecondterminalV station Aover theY transmission channel, apparatus,v eiective upon and controlled by the beginning of` transmission of signal current from the repeater station to the first Vter-- minal station to send courier current tothe rst terminal station for rendering said normallyy disabled apparatus operable and for disabling said normally operable apparatus, and instrumentalities for causing the jcourier current to arrive Vat thelrst .terminal station before the arrival of the signal current transmitted from the repeater station, lsaid Vinstrumentalities in- 

